This application relates to the art of braking systems, and more particularly to an antilock brake system (ABS) modulator relay valve. The invention is particularly applicable to a tractor or tractor-trailer type vehicle equipped with an air braking system in which a vehicle operator generates a control signal to operate a brake control valve. The signal is transmitted to relay valves which communicate compressed air from storage reservoirs to vehicle brakes. It will be appreciated, however, that the invention may relate to similar environments and applications.
A modulator relay valve for ABS brake systems typically includes an impermeable or solid walled piston or flexible diaphragm that selectively moves during normal service braking to establish communication among supply, delivery, and exhaust ports. The piston is responsive to a control signal provided, for example, from a foot brake valve or trailer control valve through a double-check valve. The control signal communicates with a control volume cavity to create a pressure on the piston. Thus, by increasing or decreasing the control signal, or pressure on the piston, the piston is selectively movable. The piston actuates an inlet/exhaust valve to selectively connect the supply, delivery, and exhaust ports. In general, connecting the supply port to the delivery port causes the vehicle brakes to engage. Closing the supply port and connecting the delivery port to the exhaust port releases the vehicle brakes.
In response to an antilock control event, a solenoid control assembly provides for rapid pulsing of the brake application. That is, if an antilock event is sensed, an electronic control unit sends suitable signals to solenoid valve assemblies associated with the modulator. The valve assemblies provide an electro-pneumatic interface between the electronic control unit (ECU) and the air brake system. If an impending wheel lock-up is sensed, the antilock controller immediately begins to modify brake application using the modulator.
Air in the control volume cavity is controlled by selectively opening and closing the supply and exhaust solenoid valve assemblies. Coils associated with the respective solenoid valve assemblies are quickly energized or de-energized in a predetermined sequence by the controller. When the solenoid coil is energized, a core or shuttle is moved to either open or close an associated air passage. This either opens or closes the exhaust passage or reapplies air pressure to the brake actuator. By opening or closing the solenoid valves, the anti-lock controller simulates brake xe2x80x9cpumpingxe2x80x9d but at a rate substantially faster than the driver of a vehicle could actually pump the brakes to avoid skidding.
In known prior art systems, the control signal provided by the foot brake valve on the trailer control valve enters the modulator through a control port. The pressure signal then passes through a small dimensioned, solenoid channel located in an axial center of the solenoid and into the control volume cavity. This arrangement can be problematic should the control signal contain any contaminants. If contaminants reside or build up in the solenoid channel, the channel may become blocked and/or the solenoid valve may not operate as desired.
Releasing the pressure from the control volume cavity in known systems occurs through an orifice exhaust solenoid passage, which is relatively small and limits the amount of air that can be rapidly exhausted. As will be appreciated, the ability to rapidly exhaust air from the control valve cavity is directly related to the performance of service and ABS brake applications. In co-pending U.S. patent application Ser. No. 09/410,519, a quick release exhaust valve was added to the modulator for use during an ABS event to improve ABS performance. However, service brake exhausting from the control volume cavity still occurs through the orifice exhaust solenoid passage.
Thus, any improvement that addresses rapid exhaust during service brake application and limits the undesirable effects of contaminants would be desirable, particularly if easily incorporated into an existing modulator valve without substantial modification.
In accordance with a preferred embodiment of the invention, an improved modulator relay valve assembly for selectively controlling brake application to an associated brake chamber is provided that improves service brake operation and effectively removes contaminants.
A preferred modulator relay valve assembly comprises a housing having a supply port, a delivery port, a control port, and an exhaust port. A piston is received in the housing defining a control volume and is in communication with the control port. The piston is movable to control communication among the supply, delivery, and exhaust ports. A quick release valve with a direct passage to atmosphere is in communication with the control volume. The quick release valve is biased toward an open position allowing communication from the control volume to atmosphere during service brake and ABS brake applications to quickly exhaust pressure from the control volume on the piston.
In accordance with another preferred embodiment of the present invention, a valve assembly for rapidly releasing control pressure during service braking in ABS applications is provided. The valve assembly comprises a housing having a supply port, a delivery port, a control port, and an exhaust port. A piston is received in the housing defining a control volume and is movable to control communication among the supply, delivery, and exhaust ports. A quick release valve extends from the control volume to provide a direct exhaust passage to allow pressure to rapidly escape from the control volume only through the quick release valve during normal service braking and ABS braking. A hold solenoid valve between the control port and the quick release valve is normally biased toward an open position for allowing communication therebetween. An exhaust solenoid valve between the hold solenoid valve and the quick release valve provides a direct passage to atmosphere. The exhaust valve is normally biased toward a closed position for preventing communication therethrough with atmosphere.
According to yet another aspect of the present invention, a method of quickly exhausting a control volume in an antilock braking system is provided. The antilock braking system includes a hold solenoid valve and an exhaust valve operatively associated therewith. Further the antilock braking system has control, supply, delivery, and exhaust ports selectively regulating supply of air to brake chambers associated with the wheels. The method comprises the steps of connecting the supply and delivery ports for braking in response to a signal at the control port, and connecting the delivery and exhaust ports to release the brakes. At least a portion of the air from the control volume is directed between service brake applications through a quick release valve into the atmosphere to enhance service brake operation.
In accordance with another aspect of the present invention, a valve assembly for rapidly releasing control pressure during service braking in ABS applications is provided. The valve assembly comprises a housing having a supply port, a delivery port, a control port, and an exhaust port. A piston is received in the housing defining a control volume and is movable to control communication among the supply, delivery, and exhaust ports. A non flow-through hold solenoid valve between the control port and the control volume is capable of preventing communication therebetween upon actuation. An exhaust means for releasing a pressure from the control volume during service braking and ABS braking is provided.
A principal advantage of the present invention is the ability to improve ABS and service brake performance in air brake systems.
Another advantage of the present invention resides in the ability to achieve improved exhaust of control air from the relay valve control cavity without increasing the size and power constraints associated with the present solenoid valve assembly.
Another advantage of the present invention is the ability to direct a control signal to a control volume cavity without passing through a solenoid valve channel or passage.
Still another advantage of the invention is the ability to easily modify the existing system to incorporate this feature.
Yet another advantage of the present invention is the ability to expel contaminants from the control volume during service and ABS brake applications.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon reading and understanding of the following detailed description.